As display terminals for information visualization such as CRT and LC monitors become widespread, there is an increasing possibility that the reflection of extraneous light in the use environment impair operators' eyesight, at worst causing asthenopia and sight weakening. There is a demand for visual display terminals having minimized reflection of extraneous light. This problem is often solved by applying antireflection films directly to visual display terminals. Typical antireflection films are laminates of high and low refractive index layers with controlled thickness that reduce the reflectance by utilizing the interference of incident light.
In the prior art, physical means of depositing inorganic oxides or fluorinated inorganic compounds in multilayer fashion by vacuum evaporation or sputtering are commonly used as disclosed in JP-A 6-11601, JP-A 7-60856 and JP-A 2000-284235. Since an expensive vacuum evaporation apparatus or sputtering apparatus must be employed in the manufacture of antireflection film-bearing articles and too much processing time and cost are needed, this approach is difficult to apply antireflection films to visual display terminals at low cost.
On the other hand, chemical means of applying coating compositions comprising organic silane compounds, inorganic fines and the like in multilayer fashion as described in JP-A 2001-293813 have advantages including elimination of expensive apparatus. In the practice of this chemical approach, titanium oxide and other oxides for imparting a high refractive index are generally employed in the high refractive index coating composition as described in Japanese Patent No. 3,031,571 and JP-A 2000-204301. Most often, photo-curable coating compositions comprising a titanium-containing alkoxide, inorganic fine particles and a polyfunctional acrylate or epoxy compound are used. See JP-A 2000-6402, JP-A 2000-47004, JP-A 2000-143924, JP-A 2000-266908, JP-A 2000-329903 and JP-A 2001-164117.
As the low refractive index coating composition, compositions containing fluorinated compounds are customary as described in Japanese Patent No. 2,800,258 and JP-A 10-147740. However, most of these compositions need heat treatment by which the substrate is limited, and suffer from problems including a long curing time and a low hardness.
To solve these problems, photo-curable materials containing fluorinated compounds are utilized as described in JP-A 8-313704, JP-A 2001-264508, JP-A 2002-22905, JP-A 2002-53804, JP-A 2002-53805, and JP-A 2002-69426. Also, photo-curable materials containing metal oxide fine particles are utilized for the purpose of increasing hardness as described in JP-A 2001-316604. However, there is a problem that no coatings can be formed on coatings of fluorinated materials, which is inadequate for antireflection films of the transfer type which require to form a high refractive index layer on a low refractive index layer.
There is a desire to have low refractive index coating compositions other than fluorinated materials. JP-A 2001-31891 discloses a coating composition comprising an inorganic oxide sol and a silane coupling agent; JP-A 2000-79600 and JP-A 2001-163906 disclose a method of forming a nano-porous structure using a silica sol having a particle size of 50 to 100 nm and a polyfunctional acrylate; and JP-A 2000-17099 discloses a method of forming a film with micro-voids or spaces. These methods are not so successful in lowering the refractive index.
JP-A 2001-233611 and JP-A 2002-79616 disclose the use of hollow silica sol, which is successful in lowering the refractive index, but suffers from problems like a need for heat treatment, limited substrates, and a long curing time.
From the past, a method of imparting the desired function to a primary substrate by laying a functional film on another substrate film and transferring it to the primary substrate is known in the applications to impart surface protection and photo-catalysis functions as described in JP-A 9-227169, Japanese Patent No. 3,225,859 and JP-A 2001-315285. No proposal has been made in the application to impart an antireflection function.